The critical dimension (CD) of a feature on a semiconductor wafer, or any product fabricated using semiconductor processing techniques, is a width of that feature. The pitch is generally defined as a critical dimension plus the distance to the next feature.
For semiconductor process methods using etch techniques, lithographic masking layers, such as for example photoresist layers, can be formed on top of the material to be etched. Photoresist layers define the desired features, masking the portion of underlying layer which is not to be etched, and leaving exposed the portion to be etched. During the etching process, materials from a portion of the layer which is etched, as well as compounds formed by various combinations of the etchant gases, the lithographic mask, and the materials of the layer to be etched, can tend to coat the sides of the desired feature, and the lithographic mask, and thereby increase the critical dimension of the feature beyond that defined immediately under the lithographic mask. Such growth of the critical dimension can disadvantageously diminish the space between the features and thereby adversely affect the functionality of the features.
As is known in the art, lithographic masks can include by way of example only, (i) soft masks such as photoresist masks, e-beam resist masks, x-ray resist masks, and syncotron particle acceleration resist masks, and (ii) hard masks, such as metals and oxides of metals such as silicon dioxide (SiO2). However, such soft and hard masks have not been found to be particularly useful in controlling the critical dimension growth.
Accordingly, there is a need to provide a semiconductor processing methodology which allows for the desired features to be appropriately etched without causing a growth of the critical dimension of the feature during the etching process.